My objective is to develop a model system in which to study the role positional information (P.I.) plays in the construction of a nervous system. In the first year of this proposal we have studied a group of mechanoreceptors called clavate hairs found on abdominal sensory appendages of crickets. The form and position of the sensory neuron presynaptic terminals reflects the position of the neuron cell body in the periphery. Thus the pattern of receptors seen at the periphery has a topographic representaton in the CNS. This is the first such topographic map to be seen in arthropod neuropile. It is also the first case in any system where the component neurons of a topographic map system are uniquely identifiable. In order to prove that the neurons are behaving in ways consistent with previously generated models for the development of the insect epidermis, a number of surgical experiments are in progress. The surgery consists of ablations, rotation or transplantations of bits of epidermis to test the effects of altering a cell's position in body coordinates on the expression of its developmental program. Thus far we have successfully carried out a number of such experiments. We have shown that when the axons are transected, the sensory cells will regenerate to their "proper" place in the CNS. We then exchanged a left sensory appendage for a right one - this misaligns the mediolateral axes of host and grafted tissue. In this experiment neurons often take unusual routes into the CNS, but their central arbors are still elaborated at proper positions in the central map. Although further experiments are necessary, these results suggest that neurons are using positional information obtained in the periphery to determine where to go in the CNS.